Eat Your Vegetables! Avoid a Stroke?
Abstracts & Commentary
By Matthew E. Fink, MD, Vice Chairman, Professor of Clinical Neurology, Weill Cornell Medical College, Chief, Division of Stroke and Critical Care Neurology, NewYork-Presbyterian Hospital. Dr. Fink reports no consultant, stockholder, speaker's bureau, research, or other financial relationship with any company related to this field of study.
Synopsis: Increased fruit and vegetable intake, at least 5 servings per day, is associated with a reduced risk of stroke.
Sources: He FJ, et al. Fruit and Vegetable Consumption and Stroke: Meta-Analysis of Cohort Studies. Lancet. 2006;367:320-326; Howard BV, et al. Low-Fat Dietary Pattern and Risk of Cardiovascular Disease: The Women's Health Initiative Randomized Controlled Dietary Modification Trial. JAMA. 2006;295:655-666.
Dietary supplementation targeted to reduce the risk of stroke and other cardiovascular diseases has been an area of much controversy in research, especially since the publication of negative results from The Vitamin Intervention for Stroke Prevention (VISP) randomized, controlled trial (JAMA. 2004;291:565-575), which studied the impact of high doses of folic acid, pyridoxine (vitamin B6), and cobalamin (vitamin B12) on vascular outcomes during 2 years of follow-up. In spite of the negative results from the VISP trial, folate/B6/B12 supplementation is widely prescribed by neurologists as part of a stroke prevention protocol, with the belief that there were many methodological weaknesses of the VISP study. Another possible explanation is that the benefits of diet depend on the complex mixture of vitamins, minerals, antioxidants, and fiber that are present in whole fruits and vegetables, rather than from a few specific vitamins that are administered as supplements.
Two recently published studies have looked at the effects of healthy diets on the risk of stroke and other cardiovascular diseases. He and colleagues from St. George's University of London performed a meta-analysis of 8 prospective cohort studies that included 257,551 individuals followed for an average of 13 years, and compared individuals who consumed less than 3 servings of fruit and vegetables per day, with those that consumed either 3 to 5 servings per day, or more than 5 servings per day. The relative risk of stroke was reduced in the 2 groups that had a higher daily consumption of fruits and vegetables—0.89 (95% CI, 0.83-0.97) and 0.74 (95% CI, 0.83-0.97, respectively). In real terms, those that consumed more than 5 servings per day had a 26% reduction in their risk of stroke. What elements in whole fruits and vegetables contribute to a reduction in stroke risk? Is it a specific vitamin or mineral, or is it related to other lifestyle changes? Individuals who eat more fruit and vegetables will probably have lower rates of smoking, a lower intake of salt and saturated fat, higher levels of physical exercise, and are less likely to be overweight.
A second important study, just published by Howard and colleagues, as part of the Women's Health Initiative, reported the results of a randomized clinical trial of dietary modification in 48,835 postmenopausal women, aged 50 to 79 years, designed to reduce fat intake to 20% of calories and increase intake of fruits and vegetables to 5 servings per day. The control group received diet-related education materials. The patients were followed for a mean of 8.1 years, and the primary outcome measures were fatal and non-fatal coronary heart disease (CHD) and a composite (CVD) of heart disease and stroke. The numbers who developed CHD, stroke, and CVD (annualized incidence rates) were 1000 (0.63%), 434 (0.28%), 1357 (0.86%) in the intervention group and 1549 (0.65%), 642 (0.27%), and 2088 (0.88%) in the comparison group. The differences between the groups were not statistically significant, although there was a trend toward greater reduction in CHD risk in those with higher intakes of fruit and vegetables.
How do we interpret these large, well-designed, and well-executed studies? Does diet really have any impact on cardiovascular and stroke risk? The VISP study looked at recurrent stroke risk over a 2-year period of time, a very short period of time to evaluate the effects of a dietary manipulation. The Women's Health Initiative followed healthy women for a period of 8 years, and the He et al study looked at cohorts
followed for an average of 13 years. It appears that the longer a dietary manipulation is followed, the more likely it is that a significant impact will be identified. Therefore, the preponderance of evidence still supports the benefits of increasing fruit and vegetable intake in order to reduce stroke risk. What specific vitamins or other nutrients are most important remains to be determined by further research, but certainly, we as neurologists can feel confident in advising our patients: "Eat your vegetables"!